Open center control valve

ABSTRACT

A hydraulic power brake booster powered by power steering gear pump pressure and utilizing an open-center valve so that fluid flows through the booster without pressure reduction when the booster is not activated. The valve assembly includes a radially floating valve seat which provides for self-centering, permits a valve separation operation to pass viscous cold hydraulic fluid or any elements which may tend to overly restrict the valve. It also includes a valve face design providing entrance and exit angles defining a venturi-type passage conducive to laminar flow with consequent reduction in valve noise, and has a hydraulic reaction mechanism which includes an arrangement for supported line pressure.

0 w rte States Patent 1 1 1 1 3,787,029 Shellliause 45 Jan, 22, 1974OPEN CENTER CONTROL VALVE 2,840,336 6/1958 Suthann 251/360 x R ldL.Shlh,V [75] inventor 2?: e] ause andaha Primary Exammer-Amold RosenthalAttorney, Agent, or FirmW. E. Finken et al. [73] Assignee: GeneralMotors Corporation,

t t, Mich- [57] ABSTRACT [22] Filed: Sept. 13, 1971 A hydraulic powerbrake booster powered by power steering gear pump pressure and utilizingan open- [211 App]' 179682 center valve so that fluid flows through thebooster Related U.S. Application Data without pressure reduction whenthe booster is not ac- 2 Division f Set NO 76,473, Sept 29, 1970, Pat Notivated. The valve assembly includes a radially floating 3,699,630,valve seat which provides for self-centering, permits a valve separationoperation to pass viscous cold hy- [52 US. Cl. 251/333, 251/363 drauliefluid er y elements which y tend to Overly [51] Int. Cl. Fl6k 47/02restrict the valve- It ls n lu s a alve fa e design [58] Field ofSearch..; 251/333, 363 p viding entrance and exit angles defining aventuritype passage conducive to laminar flow with conse- [56] Ref Cit dquent reduction in valve noise, and has a hydraulic re- UNITED STATESPATENTS action mechanism which includes an arrangement for 2,927,7373/1960 Zeuch et al 251/333 x Supponed hne pressure 2,330,610 1 Claim, 3Drawing Figures 9/1943 Natter 251/360 X PATEMEB NH 3. 787, 029

INVENTOR,

Pom/0'1? SAM/muse ATTORNEY OPEN CENTER CONTROL VALVE This is a divisionof Ser. No. 76,473, filed Sept. 29, 1970 now US. Pat. No. 3,699,680. Theinvention relates to a hydraulic power brake booster open-center valvearrangement, and more particularly to one in which a conical valve seatand valve face are constructed so as to provide a venturi-type passagewhich improves laminar flow through the valve.

The valve seat is mounted in the power piston so that it is rediallymovable when the valve member engages the seat to position the valveseat concentrically with the valve input member. This insures aconcentric annular valve opening which will also minimize valve noise aswell as provide consistent valve controlling action.

IN THE DRAWINGS FIG. 1 is a schematic representation of a vehicle powersteering and braking system embodying the invention.

FIG. 2 is a cross section view of the hydraulic brake booster used inthe system of FIG. 1.

FIG. 3 is an enlarged view of the valve input member portion of theopen-center valve provided in the booster of FIG. 2.

In the system shown in FIG. 1, the power steering pump is provided witha hydraulic fluid reservoir 12 connected to the input side of the pumpby conduit 14. The pump output conduit l6'is connected to the powersteering gear 18, which is of the open-center type so that in theat-rest position hydraulic fluid is pumped freely through the gear. Theconduit connects the output side of the power steering gear 18 with theinlet 22 of the hydraulic power brake booster 24. The booster outlet 26is connected to the sump or inlet side of the power steering pump 10 byconduit 28, thus completing the hydraulic fluid circuit.

The booster 24 is connected to actuate a master cylinder assembly 30which provides brake pressure to the front brake system 32 and the rearbrake system 34 of the vehicle in which the hydraulic system isinstalled. The booster 24 is also shown as being provided with anelectro-hydraulic pump 36 which isactuatcd when necessary to providesufficient hydraulic fluid flow and pressure availability to operate thebooster 24 when insufficient hydraulic fluid flow and pressureavailability is provided through conduit 20. The pump 36 is arranged tobe actuated as necessary, and may, for example, be actuated by a flowswitch 38provided in one of the conduits, such as conduit 28. Thebooster assembly 24 is schematically illustrated as being controlled bythe vehicle brake pedal 40.

The booster assembly 24 is illustrated in detail in FIG. 2. The housing42 is formed to provide a cylinder 44. The rear end 46 of the cylinderprovides for booster mounting by means of studs 48. Cylinder rear end 46is also formed to provide a rearwardly extending sleeve 50 which isprovided with a bore 52 extending through the sleeve and rear end 46 andaxially aligned with the cylinder 44. The forward end 54. of the housing42 has a cylinder cover which is centrally apertured at 56 so that thebooster output push rod 58 extends therethrough and is reciprocablymoved when the brake is operated. A suitable seal 60 is also mounted incover 54. The cylinder seal 62 is provided with a seal support plate 64fitting against the inner wall of the cover 54,

and a seal expander 66 on the cylinder side of the seal.

The brake pedal assembly 40 acts through the push rod 68 to actuate thebooster. The forward end of push rod 68 is connected to input member 70which is slidably received in bore 52 of sleeve 50 and extends into thecylinder 44. The inner portion of bore 52 is provided with an O-ringseal 72 and a V-block seal 74 which effectively prevent leakage ofhydraulic fluid between input member 70 and bore 52. A suitable boot 76is also mounted over sleeve 50 and push rod 68 to prevent contamination.

The cylinder 44 is dividedby a power piston 78 into an inlet or powerchamber 80'and an outlet or exhaust chamber 82. Piston 78 isreciprocably movable in cylinder 44 during brake booster operation andis urged to the brake release position by spring 83. The piston includesa sealed skirt section 84 which fits cylinder 44, and has at itsrearward end a positioning abutment sleeve 86. This sleeve is of smallerdiameter than the skirt section 84 and is suitably. notched as at 88 topermit full fluid communication between all portions of the inletchamber 80. Piston 78 is also provided with passage meansinterconnecting the inlet chamber 80 and the outlet chamber 82, thepassage means including a passage 90 extending through the piston walland a stepped recess 92 which mounts the valve and reaction mechanism.The valve mechanism controls the flow of hydraulic fluid from the inletchamber 80 to the outlet chamber 82 through the passage means, therebycontrolling the pressure differential across the power piston 78. Thelarger rearward portion of recess 92 provides a mounting for the valveseat 94. The forward end 96 of valve seat 94 abuts against a shoulder 98formed as a part of stepped recess 92. A valve seat spring retainer 100fits in the outer end of recess 92 and engages the valve seat 94 so asto position the valve seat against axial movement relative to the powerpiston 78. The valve seat has a cylinder-like skirt section 102 which isthe section between recess shoulder 98 and retainer 100. The outerperiphery of skirt section 102 is of substantially less diameter thanthe portion of recess 92 in which it fits so as to provide for radialmovement of the valve seat. Retainer 100 engages the valve seat andpermits such radial movement while tending to hold the valve seat in anyradialposition to which the valve seat is moved through its spring-likeaction urging the valve seat end 96 against shoulder 98. i

The valve seat skirt section 102 has a cylinder 104 formed by theinterior'wall thereof. Also, cylinder section 106 is formed in theforward part of stepped recess 92 and is of smaller diameter thancylinder 104. Stepped recess 92 also includes anintermediate cylindersection 108 and the shoulder 98. A reaction piston 110 has a smalldiameter forward land 112 received in cylinder section 106 and rearwardlarger diameter land 1 14 received in cylinder section 104. A portion ofreaction piston 1 10 between the lands is stepped to provide a mountingfor the reaction piston snubber 116. Snubber 116 is positionedincylinder section 108 and cushions forward movement of the reactionpiston 110. A groove 118 in power piston 78 fluid connects inlet chamber80 with cylinder section 108 so that the reaction piston 1 l0 and thecylinder section 108 cooperate to define a reaction chamber 120.Reaction piston 110 is generally cup-shaped and its forward face 122 atland 112 is provided with axially extending passages 124 which fluidconnect outlet chamber 82, through passage 90 and the forward portion ofrecess 92, with the downstream side of the valve seat 94. A snubberpiston 126 is secured to the rear side of reaction piston face 122 andextends rearwardly in a manner and for the purpose described below. Asupported line pressure spring 128 is positioned within reaction piston110 and valve seat 92 so as to urge the reaction piston forwardlyrelative to the valve seat against the force of pressure in reactionchamber 120.

Valve seat 94 includes a frusto-conical seat face 130 with the largerface opening extending rearwardly and the smaller face opening extendingforwardly. The seat face is aligned coaxially with the power piston 78,the input member 70, the stepped recess 92, the reaction piston 110, thesnubber piston 126, and the output push rod 58. The seat face isconstructed so that it extends at an angle of 30 degrees to the commonaxis 131 of these elements.

The input member 70 includes a valve 132 formed to provide afrusto-conical valve face 134 which is poitioned to mate with and extendthrough valve seat face 130. For descriptive purposes the valve andvalve seat faces will be referred to as being conical, it beingunderstood that this term encompasses a conical section formed by thefrustum of a right circular cone. At the rearward side of valve 132, theinput member 70 is provided with a snap ring 136 and immediately behindthe snap ring is a valve return bumper 138. The bumper is formed of arubber-like material and prevents the snap ring from directly contactingthe housing rear end 46, thereby cushioning the valve return and furthereliminating valve operating noise. A valve return spring 140 seats onsnap ring 136 at one end and on valve seat retainer 100 at the other endto urge the valve faces apart and, therefore, position the valve 132 inrelation to the cylinder end wall 46 when the booster is at rest. Theforward end of input member 70, forward of valve face 134, is providedwith an end section 142 located within the chamber formed by recessedreaction piston 110 in which spring 128 is positioned. The end sectionis provided with a cylinder-like recess 144 which is somewhat larger indiameter than snubber piston 126. The rear end of snubber piston 126extends slightly into recess 144. A rubber-like snubber 146 is receivedat the bottom of recess 144 and is slightly spaced from the sphericalend of snubber piston 126 when the booster is at rest.

The valve face 134 of valve 132 is comprised of a face forward surface147 and a face after surface 148 which join at the circumferential lineof contact 150. The forward and after face surfaces are frusto-conical,with the forward surface 146 forming the angle a" relative to the axisof the valve, this angle being nominally 31 degrees. The face aftersurface 148 forms the angle b" relative to the axis of the valve and isnominally 29". This arrangement, with angle of seat face 130 nominallyat 30, provides a venturi-like valve opening. By providing the properentrance and exit throat angles relative to the metering point definedby the valve circumferential line of contact 150, with the valve facesbeing smoothly finished, a satisfactorily low valve noise level isachieved. The relative valve throat angles have been found to becritical in that they should differ no more than percent in relation tothe nominal angle of the valve seat face. Since it is desired thatabrupt changes in direction of fluid flow through the valve should beminimized, it is preferable to have the valve seat face nominal angle beat about 30.

When the system is at rest, with the power steering pump 10 beingdriven, hydraulic fluid is permitted to flow freely through the powersteering gear 18 and the booster 24 and return to the pump withoutrestriction. When the vehicle is steered leftwardly or rightwardly, thepower steering gear 18 operates to build up a back pressure in conduit16 and establish a pressure differential to provide power to thesteering gear, as is well known in the art. When the vehicle brake isactuated by depression of the brake pedal 40, the input member movesforwardly, closing the space between valve seat face 130 and valve face134. Initial closure will result in contact of the valve 132 with thevalve seat face 130, causing the valve seat to move radially, if it wasslightly off center, to align the valve seat with the valve. Suchalignment may also occur when the brake pedal is depressed while thepower steering pump is not operating. Due to the minimal width of thereaction piston lands 112 and 114, slight radial movement of the valveseat 94 is accomplished without binding the reaction piston 110. Thelands have a pivotally sealing engagement with their respective cylindersurfaces which accommodates the valve seat radial movement.

Upon restricting the hydraulic fluid flow from the inlet chamber to theoutlet chamber 82, hydraulic pressure is built up in the inlet chamberto establish a pressure differential across the power piston 78. Theincreased pressure in inlet chamber 80 also acts in reaction chamber tourge reaction piston 110 rearwardly against the force of spring 128.This initial reaction force is not transmitted to the input member 70since the other end of spring 128 is seated on the valve seat 94. Thepressure differential also urges the power piston 78 forwardly againstthe force of piston return spring 83, overcoming that spring and movingpush rod 58 forwardly to actuate the master cylinder 30. As the pressuredifferential increases, reaction piston 110 is moved rearwardly untilsnubber piston 126 engages snubber 146. Since this normally happensquickly when the brakes are quickly applied, the movement of snubberpiston 126 rearwardly into recess 144 displaces hydraulic fluid fromthat recess in a dashpot manner, providing a cushioning effect in theinitial transmittal of reaction force to the input member 70. Furtherrearward movement of reaction piston ll0 causes the snubber 146 to becompressed as it transmits additional reaction force to the input memberas the pressure differential across the power piston 78 increases. Itcan be seen that at any required pressure differential the valve systemwill reach a poised position wherein the valve opening between faces and134 is just sufficient to maintain the required pressure differentialand resulting braking effort If for any reason the pressure should bebuilt up in inlet chamber 80 beyond a desired pressure level, thepressure relief valve 152 will open, connecting the inlet chamber withoutlet chamber through passages not shown so as to establish thepressure limit.

Upon brake release, the input member 70 is moved rearwardly by spring140, slightly opening the valve faces and permitting a decrease in thepressure differential across power piston 78. When the brake is fullyreleased, the valve 132 returns to its at-rest position with the valvereturn bumper 138 having cushioned its engagement with the cylinder rearwall 46. As the reaction piston 110 moves forwardly relative to powerpiston 78 upon brake release, it is similarly cushioned by snubber 116.i

When the vehicle in which the booster is installed is operated duringvery cold weather, the booster must allow for the pressure influence ofthe cold viscous oil being pumped through the valve without applying thebrakes and causing a dragging brake operation even though the vehicleoperator has not applied the brakes. This is accomplished by allowingthe power piston 78 to move slightly under the pressure influence of thecold viscous oil withoutpulling the valve 132 with the piston. Thisslight piston travel results in an increased valve opening before thepiston travel is sufficient to apply the brakes through the mastercylinder. This amount of piston travel is most' easily provided for byestablishing the length of push rod 58 so that the rear end of the pushrod is slightly disengaged from the power piston when the booster is inthe condition shown in FIG. 2. This is easilyaccomplished since theforward position of push rod 58 is determined by the master cylinderstop acting to position the master cylinder piston. This positioning ofthe master cylinder piston against a stop is well known in the mastercylinder art.

The separating valve arrangement also minimizes the piston travelnecessary to actuate the booster unit since the at-rest valve openingcan be set for warm hydraulic fluid operating conditions which usuallyexist after the pump has been pumping the fluid through the system for atime. The action of the separating valve described above is alsoadvantageous when foreign material is entrained in the hydraulic systm.If, for example, a piece of rubber-like material or a small metalparticle becomes so entrained, the foreign element will lodge in thevalve opening, producing a reaction similar to that of the cold viscousoil, causing a slight buildup in pressure which moves the power pistonto open the valve to a greater extent. This will allow the foreignobject to pass through the valve easily and not affect brake boostercontrol.

The noise level of the booster assembly relates, among other factors, tothe natural frequency of vibration of various booster components and thecyclic pressure pulses generated by valve operation. When thesefrequencies and pulses are sympathetic, noise at an objectionable levelmay be generated. It has been found, in units suitable in size forpassenger car use, that an angle c of 30 reduces the noise to anacceptable level. In heavier units, suitable for trucks, for example theangle 0 may be as much as 45. In some instances with such heavier unitsthe tapered outlet and inlet angles a and b may be omitted and the valveface angle may be the same as the valve seat angle. This is permittedwhen the natural frequencies of vibration of components aresubstantially different from the cyclic pulses, and a short valve seatface is used. When cavitationgenerated noises are at objectionablelevels, the dual valve face arrangement, giving a venturi effect,contributes to noise reduction. What is claimed is: 1. An open centercontrol valve assembly for a hydraulic brake booster comprising:

an annular valve seat formed to provide an inner peripheral conical faceextending at an angle of substantially 30 from the axis thereof andopening toward the valve assembly inlet, a valve extending into saidvalve seat and formed to provide an outer peripheral conical face invalving relation with said inner peripheral conical face and defined bya first face conical surface extending ,at an angle of substantially 29from the axis thereof and on the inlet side of said valve assembly and asecond face conical surface extending at an angle of substantially 31from the axis thereofand on the outlet side of said valve assembly,means for moving said valve relative to said valve seat to controlhydraulic fluid flow therebetween, and means permitting radial movementof said valve seat relative to said valve upon force transmittingcontact between said faces to position and retain said valve seatconcentrically with respect to and axially aligned with said valve.

1. An open center control valve assembly for a hydraulic brake boostercomprising: an annular valve seat formed to provide an inner peripheralconical face extending at an angle of substantially 30* from the axisthereof and opening toward the valve assembly inlet, a valve extendinginto said valve seat and formed to provide an outer peripheral conicalface in valving relation with said inner peripheral conical face anddefined by a first face conical surface extending at an angle ofsubstantially 29* from the axis thereof and on the inlet side of saidvalve assembly and a second face conical surface extending at an angleof substantially 31* from the axis thereof and on the outlet side ofsaid valve assembly, means for moving said valve relative to said valveseat to control hydraulic fluid flow therebetween, and means permittingradial movement of said valve seat relative to said valve upon forcetransmitting contact between said faces to position and retain saidvalve seat concentrically with respect to and axially aligned with saidvalve.